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ENERGY                                       1!
5.   How many cubic miles of ice could be melted by the heat comput in the preceding problem?   The latent heat of ice is 80 calories per gra:
6.   The winder of a spinning top is a helical spring, which is set in cylindrical piece 1 inch in diameter.   When the winder is hooked to t top and twisted through TT radians a force of 1 pound has to be applied the cylinder tangentially in order to keep it from untwisting itself.   Af1 the spring is given a twist of^J turns the top is released.   Find the kine-energy the top would acquire if there were no frictional forces.
7.   In the preceding problem find the angular velocity of the top suppc ing it to consist of a circular plate of 2 inch radius, and of J pound weig]
8.   If the top of the preceding problem turns for 2 minutes before stc ping, find the mean torque due to friction and resistance; also find t total number of revolutions made.
9.   A top is given a motion of rotation by pulling at a string wou: around it.   Derive an expression for the energy communicated, (a) wh
 the force applied to the string is constant; (b) when it varies directly wi the length of the string which is unwound.
157. Power.  Power is the rate at which work is don When put into the language of calculus this definition b comes
P = ^-                               (VI
Power is a scalar quantity and has the dimensions [ML2T~ The C.G.S. unit of power is the erg per second. This ui is too small for engineering purposes; therefore two larg units are adopted, which are called the watt and the kilowa The following relations define these units :
-,      <L<L    1 joule 1 watt = ~ -1 sec.
sec. 1 kilowatt = 103 watts
= 1010-